/* -*- coding: utf-8 -*-
 *
 * 3289.cc:  No.3289 Make More Happy Connection - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 300000;

/* typedef */

using ll = long long;

/* global variables */

int xs[MAX_N], ys[MAX_N];
ll dp0[MAX_N], dp1[MAX_N];

/* subroutines */

inline int score(int x, int y) { return (x == y) ? x : 0; }

/* main */

int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d%d", xs + i, ys + i);

  dp0[0] = dp1[0] = score(xs[0], ys[0]);

  for (int i = 1; i < n; i++) {
    int sci = score(xs[i], ys[i]);
    dp0[i] = max(dp0[i - 1] + score(ys[i - 1], xs[i]),
		 dp1[i - 1] + score(xs[i - 1], xs[i])) + sci;
    dp1[i] = max(dp0[i - 1] + score(ys[i - 1], ys[i]),
		 dp1[i - 1] + score(xs[i - 1], ys[i])) + sci;
  }

  printf("%lld\n", max(dp0[n - 1], dp1[n - 1]));
  
  return 0;
}